Prior art image sensors including one-transistor pixels are known. A pixel of such an image sensor comprises a MOS transistor formed in and above a semiconductor substrate. A buried semiconductor layer of a doping type opposite to that of the substrate is placed in the substrate under the transistor and delimits a substrate portion between the transistor and the buried layer. On lighting of the pixel, the charges originating from the capture of photons are stored between the transistor and the buried layer. The operation of this type of pixel requires the transistor drain to be electrically connected to the buried layer while the transistor source must remain insulated from the buried layer.
It may be difficult to simultaneously ensure a proper electric insulation of the transistor source with respect to the buried layer while putting in contact the drain and the buried layer.